Food
Feed a varied diet using at least 3 sources to provide enough vitamins, minerals, protein, vegetation and fibre to keep the fish healthy, growing and well conditioned.
All fish can be categorized as herbivores (consume vegetation), carnivores (meat eaters), or omnivores (either), with further classifications for piscivores (fish eaters), insectivores (insects) etc, but most fish will go by the rule that if it fits in their mouth, it can be food.
Staple foods are processed foods, either in flakes or pelleted form (use incrementally larger pieces as the fish get larger). Many special recipes exists (floating, sinking, vitamin enriched, spirulina based etc). Other commercial products are frozen foods (ie: shrimp, bloodworms, etc) and freeze dried foods (ie: grubs, tubifex worms). There are also live food cultures (ie: white worms) or collected (ie: earthworms).
Research your fish's dietary classification and try to target the fish foods you use to their tastes. When you have a conflict where you have herbivores which will get sick from a too high-protein diet being given to omnivores, switch to more algae based foods (ie: spirulina sticks) which can be eaten by both.
Feeding is a rewarding part of the hobby. A little research into what to feed and how much to feed will contribute to their better health & appearance.
A typical feeding routine is twice a day, as much as they can consume in a few minutes, allowing an hour for digestion after the last feeding, before turning off the lights. There are some exceptions to this guideline. Feed size appropriate foods (smaller than their throat and not too small to be noticed).
Don't be afraid to experiment with alternate foods. Many vegetables will be eagerly accepted. It only requires a small amount of research into selection, preparation and delivery.
Details...
One way to look at a fish's diet is to look at what they would eat in nature. I look at some conditions which improve their appetite, and how all this food becomes pollution in the aquarium. I discuss the staple dried processed foods, fresh vegetables, frozen foods, live foods and freeze-dried foods. I then wrap it up in a summary.
NATURE'S MENU
Almost every fish book discusses feeding (with some interesting variations in recommendations). One article I found very interesting (by Dr.Ghadially) was regarding their diet in nature. Knowing the diet fish evolved with provides an excellent basis to judge the processed foods available to us.
From Dr Ghadially, "One way to gain an insight into the dietetic needs of an animal is to examine, macroscopically, microscopically, and chemically, the stomach contents of specimens caught in the wild, permitting us to make certain broad generalizations regarding the nutritional and dietetic requirements of small fishes kept in aquaria."
1. Almost 1/2 of their diet is indigestible matter (roughage). While it has no nutritional value, it has some physiological importance for without it gut movement would be impaired and the animal would become constipated.
2. Most of the digestible matter in the majority of our fishes' diet comes from animal sources (ie: insect larvae, smaller fishes, daphnia, cyclops etc), so they are regarded as predominantly carnivorous or omnivorous. Some of our aquarium fish will eat a fair amount of algae and other plant life, but they too will accept some animal foods. These are predominantly herbivorous. A few fishes will only accept live or meaty foods and these are true carnivores.
3. The ratio of protein to that of fat plus carbohydrates in most fish is 1:1 (almost 1/2 of digestible matter is protein). Fish have a poor tolerance for fats, so fat should be omitted as much as possible. This is in sharp contrast to animals such as man, dog, horse or cow, who live on a carbohydrate rich diet (protein ratios of between 1:3 and 1:10).
4. In the wild, fish hunt and feed almost continuously throughout their period of activity, thus they are accustomed to small and frequent meals, and may often encounter periods of famine or feast. In an aquarium, we do not need to replicate this pattern, as the fish are less active, but it is beneficial to offer more frequent small meals than infrequent large meals.
5. We have limited knowledge on the vitamin, mineral and trace element requirements of our fishes (and vitamins are destroyed by drying & heating), so it's recommended to use foods from a variety of sources (live, fresh, frozen, freeze-dried etc).
6. Since many of our fishes have small mouths and few or no effective teeth, the
hobbyist must provide food of correct particle size. Too fine a food will be ignored
and will be a cause of pollution.
APPETITE
From William Innes: Temperature and oxygen directly influence the amount of food a fish can properly consume. The warmer they are (within their own established limits), the faster they breathe, digest, eliminate & grow. An ordinary aquarium fish will have an indifferent appetite at 67F, a good one at 72F and a ravenous one at 77F. It does not increase above 80F because of the diminished oxygen content of the water.
POLLUTION
Another consideration regarding feeding is that any food dropped into an aquarium, feeds the nitrogen food chain (regardless of whether it was eaten or lost in the gravel). The food chain starts with ammonia, and then either gets nitrified (into nitrite and then nitrate) or it gets taken up by natural plants growing in the aquarium (any broken rotting leaves will reintroduce the ammonia back into the water). The more we feed, the more active this food chain becomes (requiring more & better filtration) and the faster it accumulates at its final product (nitrates) which requires water changes to dilute it. Very well planted aquariums will assist in the uptake of the nitrogen products, which are then removed in solid form when the plants are pruned.
DRIED PROCESSED FOODS
Pellets or flakes, the variety and quality has almost reached the point where no other food is needed. It's drawbacks are that the stability of the vitamins is poor and it deteriorates quickly when exposed to moisture. Buying in large quantities will reduce your costs, but the product will accelerate its expiration after being opened. One alternative is to use a small container in the vicinity of the tanks, which is periodically refilled from a bulk container kept in the freezer.
FRESH VEGETABLES
Many fish will accept fresh vegetables. One example:
Zucchini (slice off the rind, may have pesticides), cut a 1/2" slice of the end and attach a weight (lead strip) to sink it. Retrieve anything left after 2 days. Eagerly accepted by plecos and other algae eaters, mbuna Africans, herbivores such as Silver Dollars and many loaches.
Other fruits & vegetables commonly referenced, orange slices (Koi), iceberg and romaine lettuce, brussel sprouts, skinned peas and cucumber. Preparation might be as simple as rinsing, or chopping as appropriate. Some need to be softened first, either by blanching in boiling water or the microwave for a few seconds. As with any healthy diet, do not be afraid to experiment, and do not overfeed any one type used.
FROZEN FOODS
Either in a slab or in little cubes, the water content is usually quite high, but there is no substitute for some of the products offered in this form. The two most popular are frozen bloodworms (larvae stage of usually the midge fly or mosquito) and frozen shrimp (many types and sizes available, including newborn for fry). Typically fed by 1 of 2 methods. In a species tank (where everyone has the same chance at the food), break off a chunk and drop it into the tank. This generates a feeding frenzy and creates a small amount of pollution, which in normal circumstances is quickly consumed by the tank's bacterial population. The alternate method is to place the food while frozen in a container of room-temperature water. After thawed, the food can then be fed by a squeezed spigot (like those used in test kits), or just poured into the tank. If pouring, it is advisable to pour the excess water from the container down the drain.
Avoid frozen foods if there is evidence that it has thawed. Spoiled food can be loaded with toxins hazardous to your fish. Use thawed frozen food as quickly as possible and throw out the excess.
LIVE FOODS
White worm cultures are easily harvested. Many people hatch their own brine shrimp to keep newborn fry fed. Fresh earthworms can be prepared for fish, either by a quick rinse, or by chopping them up into size appropriate pieces. Use only fresh worms with good colour, from a safe environment. Leaving the worms for 24 hours will allow them to excrete the contents of their stomach, before feeding them to the fish. Earthworms may be frozen to facilitate breaking them into smaller pieces. Some imagination can be used in food choices with 2 cautions. Live food may come with diseases or parasites, especially if harvested from a freshwater habitat. The immune system of a tropical fish is often not up to the task of a strange foreign (to them) attacker. The other caution is that nature provides creatures with a degree of protection by making many of them poisonous. Avoid spiders, snakes, newts, bees, hornets and some ants. Also note that while the larvae stage of many insects is ideal for fish to eat, some insects have an aquatic stage which is predatory to fry or smaller fish. You might also encounter a few bugs hatching in your tank and flying around inside your canopy.
FREEZE-DRIED FOODS
The heating/freeze-drying process kills most if not all harmful organisms, preserves the flavour and nutritional value, eliminates about 90% of the weight by removing the water, and the finished product will resist deterioration if kept dry. Fish may not readily eat it due to the texture, so feeding rings, perseverance and some patience may be needed. As with any food, variety is the key, so if your fish accept some of the products available in freeze-dried format, you will have much more flexibility in a convenient off-the-shelf package.
SUMMARY
From the information above, we can deduce several strategies. Feedings should be size and quantity appropriate, using a wide variety of sources which include high-protein foods, high-fibre and low-fat. The higher the temperature, the greater the appetite. The more we feed, the more filtration needed.
In practical terms, one extreme would be a grow out tank of newly hatched fry, which would follow the strictest regiment, using warm water (for growth), extreme caution with size appropriate food (or they can't eat) and quantity appropriate amounts (or their water may quickly foul), using very small portions (small fish) frequently (ie: fed every 2-3 hours as an example).
At the other extreme, with a few adult fish in cool water (ie: Goldfish at 68F), a feeding could be done once every couple of days.
Most aquariums operate at a mid-point, with a wide variety of fish living at different levels of the tank, with some variation in dietary requirements, 77F, good to average filtration, 10 to 12 hours of lighting. A typical feeding regiment would be a staple food in the morning (if you only feed once, then it should be in the morning) consisting of flakes and/or pellets (as appropriate to the fish). Feed as much as can be eaten in a few minutes. For small fish like many tetras, about 5 minutes. For very aggressive eaters, gauge the quantity using your experience, by what you are dropping in and the appearance of their stomach. Using size appropriate pellets, 2 to 3 pellets per fish is an appropriate starting point.
While the morning meal is often done by a battery powered automatic feeder or during the rush to get out of the house to get to school or work, the evening meal is the hobbyist's opportunity to catch up on what has been happening in the aquarium. For feeding, it's the time when we ensure that all the fish are being fed properly. This is done by target feeding and by using select foods. A cube of freeze-dried tubifex worms pressed against the glass will be appreciated by tetras. A few bottom-feeder pellets thrown towards the back of the tank will be taken up by your Corys and Loaches, an algae wafer for your algae eaters, spirulina sticks for your other herbivores, beefheart for the Discus, bloodworms for Angelfish & Bettas, and brine shrimps for almost everyone.
In a mixed community, everyone will be attracted to foods which are perhaps not intended for them, making feeding a bit of a challenge sometimes. Nocturnal feeders such as Raphael catfish and many Eels & Knifefish should be given their meal just before the lights go out (while normal feeders should be given an hour to locate all their food and digest a bit). It may become very difficult to get any food past very aggressive eaters (Danios, Monos, some Rainbowfish, Oscars, Goldfish, Venustus and some other cichlids) to the less aggressive eaters (Gouramis, Tetras, Corys, Knifefish, Eels, Angelfish, Discus, Apistos, some loaches, Plecos). Various techniques exist, using very different sized pellets, foods which appeal less to the aggressive fish, hiding food, feeding from multiple locations simultaneously, dropping food down a pipe to a protected area, etc etc, but sometimes the best solution is to just not put incompatible eaters in the same tank. If you suspect an incompatibility, give them a few days to see if they adjust. Sometimes the meek develop the needed mean streak to bully in on the food (ie: Angelfish, Discus, some Loaches, and Tetras).
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